The present invention relates to a measurement pipe for an electromagnetic flowmeter used for measuring the flow rate of a conductive fluid.
In an electromagnetic flowmeter employing the Faraday law of electromagnetic induction as its measurement principle, excitation coils and a pair of electrodes are arranged in a measurement pipe such that the magnetic fields of the coils, the axes of the electrodes, and the axis of the measurement pipe are perpendicular to each other. In this arrangement, the flow rate or average flow velocity of the measurement target fluid is measured by extracting an electromotive force generated in the conductive measurement target fluid flowing in the measurement pipe by the electrodes.
In general, a measurement pipe is made of a nonmagnetic material such as stainless steel. To prevent the short circuit of the electromotive force generated in the conductive measurement target fluid, as shown in Japanese Utility Model Publication No. 2-28411 (reference 1), insulating coating with a lining material is performed for the inner surface of the measurement pipe which serves as a liquid contact surface with the measurement target fluid, and the outer surfaces of flanges integrally formed at the openings of the two ends of the measurement pipe, i.e., those surfaces of the flanges which are to be connected to pipes (to be referred to as pipe connection end faces hereinafter).
An electromagnetic flowmeter used for processes is often exposed to various types of fluid conditions, e.g., the temperature, pressure, whether a corrosive/slurry component is present, or the like. Accordingly, as the lining material, an expensive material having an excellent heat resistance, corrosion resistance, electrical insulation, and the like, e.g., fluoroplastic, is used. In an electromagnetic flowmeter whose application is limited for measuring water, an inexpensive material such as chloroprene rubber is used as the lining material.
The conventional lining materials as described above, however, do not adhere to the measurement pipe well, and can be separated from the measurement pipe easily. For this reason, as shown in FIG. 3, a reinforcing pipe 2 formed of a punching plate (porous plate) is attached in a measurement pipe 1 in advance through a ring 3, and is covered with a lining material 4. This increases the mechanical bonding strength of the lining material 4 and measurement pipe 1 to prevent separation of the lining material 4 and deformation or the like of the lining material 4 caused by temperature change or pressure change in the measurement pipe 1. A lining material reinforcing structure like this is described in the above reference 1, Japanese Patent Laid-Open Nos. 61-294316 (reference 2) and 61-271419 (reference 3).
As a structure for preventing separation of the lining material 4 from the flange portions, as shown in FIG. 3, part of the open surfaces of annular grooves 6 formed in pipe connection end faces 5a of flanges 5 are covered with ring plates 7. Hence, the ring plates 7 prevent separation and removal of the lining material 4 filled and solidified in the annular grooves 6. Reference numerals 8 denote electrodes; 9, compression coil springs for pressing the electrodes 8; 10, tube-like caps for accommodating the electrodes 8 and compression coil springs 9; 11, saddle-shaped excitation coils; 12, a signal lead wire; and 13, a conductive measurement target fluid.
As described above, as the conventional lining material does not adhere to the measurement pipe 1 well, the reinforcing pipe 2 must be fixed to the inner surface of the measurement pipe 1 through the ring 3, and the annular grooves 6 must be formed in the pipe connection end faces 5a of the flanges 5 and the ring plates 7 must be welded to the annular grooves 6. This increases the number of components, the number of manufacturing steps, and the number of assembling steps of the electromagnetic flowmeter, leading to a further increase in the manufacturing cost.
When the lining material is a fluoroplastic, with general injection molding (with a comparatively high speed and high pressure), when the resin is cooled to solidify and shrinks during crystallization, a large stress is left. Therefore, the cold flow characteristics (a creep deformation, among those occurring when a load is continuously applied for a long period of time, which occurs in room temperature or less) in normal temperature and under normal pressure are poor, cracking or fracture tends to occur easily, and the sealing performance for electrode attaching holes 14 decreases. As a countermeasure against these problems, collars 8A of the electrodes 8 are urged against annular lining portions 4a covering the peripheral portions of the outer openings of the electrode attaching holes 14 by the compression coil springs 9, respectively, thereby sealing the electrode attaching holes 14.
When the collars 8A are always urged with the spring pressures, however, the lining portions 4a cause compression deformation to decrease the electrode-to-electrode distance, and outputs extracted from the electrodes 8 decrease. In addition, as the caps 10 are formed cylindrically and accommodate the electrodes 8 and compression coil springs 9, they project from the outer surface of the measurement pipe 1 largely. Chloroprene rubber has a low heat resistance and tends to wear easily due to the excessive elasticity, so that its use is limited depending on the application. A manufactured product needs further manual processing.
From the above reasons, as a lining material, it is required to select one with a comparatively good heat resistance, weathering resistance, and corrosion resistance, which requires a low cost, has good moldability, and meets the requested specification.
It is an object of the present invention to provide a measurement pipe for an electromagnetic flowmeter, in which the cost of the lining material is reduced.
It is another object of the present invention to provide a measurement pipe for an electromagnetic flowmeter, in which components such as a reinforcing pipe, ring plate, compression coil spring, and the like become unnecessary to reduce the number of manufacturing steps, the number of components, the number of assembling steps, and the like, so that the total cost of the entire apparatus can be reduced.
In order to achieve the above objects, according to the present invention, there is provided a measurement pipe for an electromagnetic flowmeter, comprising a cylindrical pipe main body having openings at two ends thereof, a pair of flanges integrally formed with the pipe main body to project outside the openings, and a lining material made of a reinforcing-material-mixed synthetic resin to cover at least an inner surface of the pipe main body and side surfaces of the flanges.